ICES CM 1998/0:29
Theme Session Deepwater Fish
and Fisheries
International Council for The
Exploration of The Sea
Fecundity of Greenland halibut (Reinhardtius hippoglossoides)
in the north east Arctic
A.C, Gundersen, O.S. Kjesbu, A. Stene, and K.H. Nedreaas.
ABSTRACT
Because of recruitment failures and a historic low spawning stock biomass, the Northeast
Arctic Greenland halibut (Reinhardtius hippoglossoides) stock has been strongly regulated in
the 1990-ies. Fecundity, which is defined as the number of vitellogenetic oocytes developing
in each female prior to the spawning season, is important for understanding spawning-stockrecruitment relationships. The relation between the fecundity and length for Northeast Arctic
Greenland halibut stock has not been previously established.
A total of95 Greenland halibut ovaries, collected in September 1996 in the Norwegian and
Barents Sea were analysed. The Greenland halibut were mainly in maturity stage 4, that is
vitellogenic oocyte size between 2 and 4 rom in diameter. The estimated mean gonadosomatic
index (GSI) was 7.5% (range 2.0-13.5%). Fecundity ranged from 6,800 to 70,500 eggs per
female.
The fecundity-length (F (in 1000)-L (in cm» relationship is:
F = 1.155
* 10.7 * L 4.59.
(~=
0.68).
The fecundity-weight (F (in 1000) - W (in g» relationship is:
F = 2.539
Key words:
* 10" * W 1.439
(~=o.77).
Barents Sea - Fecundity - Gonatosomatic index - Greenland halibut
Agnes C. Gundersen, Mare Research, Section ofFisheries, P.O. Box 5075, N-6021 Alesund,
Norway. [phone +47 70 1113 50,fax +47 70 13 89 78, e-mail: Agnes.Gundersen@hials.noJ
Olav Kjesbu, Institute ofMarine Research, P.o. Box 1870, Nordnes, N-5024 Bergen, Norway.
[phone +475523 85 00, fax +475523 83 87].
Anne Stene, Alesund College, P.o. Box 5104, 6021 Alesund, Norway. [phone +47 70 11 12
OO,fax +47 70 13 89 78].
Kjell H Nedreaas, Institute of Marine Research, P.o. Box 1870, Nordnes, N-5024 Bergen,
Norway. [phone +4755238500, fax +4755238387].
I"~
INTRODUCTION
Greenland halibut (Reinhardtius hippoglossoides Walbaum) in the Northeast Atlantic is
distributed mainly on the continental slope off Norway from 62°N to the regions north of
Spitsbergen. It is observed down to 1400m. In other parts of the Atlantic, Greenland halibut is
observed down to 2000m (Boje 8i Hareide 1993). It is described as a boreal-arctic species and
is found mainly at temperatures between -1 ° and 4 "C. The population constitutes a separate
management unit in theICES management system.
During the late 80s a drop in the Greenland halibut year class indices, based on the regular 0group and juvenile surveys, and a historic low spawning stock biomass were observed (Hylen
& Nedreaas, 1995; Smirnov, 1995). Parallel to this, the importance of Greenland halibut as a
commercial fish species increased. There was also a decrease in the commercial catch per unit
of effort (CPUE) and this lead to strong regulations including a fishing ban north of 71°30N
from 1992.
Studies offish reproduction and stock-recruitment relations are basic issues in the work of
precautionary approach, to prevent a stock collapse. Fecundity, which is defined as the .
number of eggs developing in a female for the following spawning season (Bagenal 1978) is
important for obtaining data on population stability and year-dass strength. Generally
deepwater species along with Arctic and Antarctic species produce fewer and bigger eggs than
related boreal species (Marshall 1953). Fecundity is usually related non-linearly to total fish
length and weight. The relations are usually allometric (Bagenal 1978).
Little work has been done on ClTeenland halibut fecundity, particularly in the Northeast
Atlantic. Millinsky (1944) estimated fecundity of two Greenland halibut females in the
Barents Sea. In the Northwest Atlantic a few investigations on Greenland halibut have been
conducted. Lear (1970) examined 45 females from the Newfoundland-Labrador area;
Bowering (1980) examined 153 females from Southern Labrador and the Southeastern Gulf of
St. Lawrence. Jensen (1935) estimated the fecundity of one female in West-Greenland waters.
In East-Greenland waters a fecundity-length relationship is presented for 1996 (R.0nneberg et
al. 1998).
This paper describes the results of a fecundity study of Greenland halibut in the Norwegian
and Barents Seas. The objectives were to obtain relations between fecundity and length, and
fecundity and weight.
MATERIALS AND METHODS
The ovaries were collected in September 1996 frbm fish caught using gillnets and longlines
on the continental slope west of Bear IsI!)I1d (Fig. 1). The combined sample consisted of 95
females randomly chosen from the catches. The females were maturing with egg diameters of
2-4mm (visual), which implies that spawning would have likely occurred a few months later.
The ovaries were frozen at sea and preserved in 3.6% phosphate and then approximately one
month later stored in buffered formaldehyde.
2
Q
o
0
20·
Fig. 1.
Sampling areas for Greenland halibut used in the fecundity study. Samples were
taken during the Autumn Survey conducted by the Institute ofMarine Research,
Bergen in 1996, west of the Bear Island
The methods used in fecundity analyses are the same for whatever purpose fecundity
estimates are needed (Bagenal 1971). For the present study, the gravimetric method described
by Bagenal & Braum (1978) was used. The procedure for estimating the number of eggs in an
3
ovary was: measure the total weight of the ovary after fixation, collect 4 subsamples, store the
samples in 70% ethanol, establish a raising factor (R,.,,) for each sample based on sample
weight and ovary weight, count the number of eggs in sample 1 and 2, and estimate the total
number of eggs (defined as the fecundity) in the ovary. If the coefficient of variation (CV)
between the two samples (1 and 2) exceeded 5%, samples 3 and 4 were counted.
Raising factor was defined as (i):
(i)
R,." = GW, / SW,y
R.y =
Raising factor for ovary x and subsample y, GWx = gonad weight after fixation of ovary
x, and SW,y = subsample weight of ovary x, subsample y.
Fecundity was estimated by the equation (ii):
(ii)
F xy =
R,." * N xy
Fxy = fecundity of ovary x, subsample y, R.y = Raising factor for ovary x and subsample y,
and N = number of eggs counted ovary x, subsample y.
Gonadosomatic index (GSI) is defmed as the relation between the gonad weight (GW) (g) and
the total weight (W) (g) of the fish (iii).
(iii)
GSI = (GW *100%) / W
Hepatosomatic index (HSI) is defined as the relation between the liver weight (L W) (g) and
the total weight (W) (g) of the fish (iv).
(iv)
HSI = (LW *100%) / W
Subs ample size
An acceptable subsample size was established by comparing the fecundity obtained from an
analysis of subsamples taken from the same ovary. Subsamples of 1.7g were used due to a
coefficient of variation below 5%, corresponding to more than 200 eggs per sample.
Types of oocytes
Three types of oocytes were discovered. Vitellogenic oocytes assumed to become spawning
eggs in a few months, were defined as G 1. Oocytes of significant smaller diameter with yolk,
were defined as G2. Small previtellogenic oocytes were defmed as R (recruit group). As the
ovaries had been frozen oocyte diameter was not measured. The number of G 1 oocytes is the
fecundity estimate for an ovary.
Homogenity
Homogenity was tested by comparing four different ovarian sections; anterior, middle and
posterior section of the right lobe and the middle section of the left lobe. Five ovaries were
analysed and from each section foursubsamples were taken.
4
Data analyses
The Excel-97 was used in the data analyses.
Relations between fecundity and length and fecundity, and weight were established using loglog-transformed regression.
The coefficient of variation (CV) was used in the analyses to evaluate the fecundity estimates
(v). The coefficient of variation (%) is the standard deviation (std) of the estimates divided by
the mean fecundity (Fm,,,,) (Sokal & Rohlf 1995).
CV = (std* 100%) / F m...
(v)
RESULTS
Homogenity
The fecundity of the 5 chosen ovaries varied from 20,000 to 35,000 eggs. A comparison of the
midsections of the two lobes within each ovary, indicated a minor variability between the two
lobes. No systematic trend was, however, observed (Fig. 2). The right midsection CV was in
the range 1.3-5.5%. The CV of the left midsection was in the range 1.9-5.5%.
o Left Mid
• Right Mid
40
~
°
o.
35
0
-a
30
'""
20
' -'
'6
:::l
"""
•o
C
25
15
10
45
66
59
79
84
Ovary number
Fig. 2.
Meanfecundity (1,000) of5 subsamples studiedfor homogenity of the ovary.
Comparison of left and right lobe represented by samples taken in the midsection
of the ovaries.
No systematic difference in the fecundity estimates, based on samples from any of the four
sections was observed (Fig. 3). Therefore, subsamples from the middle section of the right
lobe were regarded as representative for the ovary, and the egg counts were based on
subsamples taken in this section.
5
<.
a)
.. + .. Right Anterior
.•• -i> •• Right
- -.
-Right Mid
'_Left Mid
posterior
.+
·8 30
-°o
1
o.
'.
'-'
.,..
25
..
20
15+---------+---------+---------~------~
66
59
45
84
79
Ovary number
b)
.. + .. Right Anterior
-Right Mid
•• -b •• Right
-o-LeftMid
posterior
9
8
§ 7
~
~
,,
~
.~
t;;
;>
6
5
""'0
4
.~
,
+-____~b~.~--------------------==~~'~~~~~~~~------5%
1:
.uOJ 3
..
~
\;::i
""'0
OJ
U
"
,, "
2
1
•••• b· ...•..•
0
45
66
59
79
84
Ovaty number
Fig. 3.
Comparison offecundity for four subsample sections (a) of Greenland halibut and
coefficient of variation (CV) of mean fecundity of the four sampling sections
. within each ovary (b). .
6
.,
The Greenland halibut females
Total length of the Greenland halibut females sampled ranged from 48cm to 80cm (Fig. 4).
The Greenland-halibut caught by longlines were on average smaller than the Greenland
halibut caught bygillnets (Fig. 4). The mean length of the gillnet samples was 67.6cm
(std=5.1, N=45), whereas the mean length of Greenland halibut sampled from longline
catches was 63.0cm (std = 6.0, N = 50). Mean length of the combined sample was 65.2cm
(Tab. 1).
Tab. 1.
Summary table for the Greenland halibut on which the fecundity studies are
conducted.
Gear
N
Mean length (em)
Minimum length
Maximum length
Std
Variance
Longline
50
63.0
48
80
6.0
36.1
_Longtine, N = 50
Gillnets
45
67.6
51
78
5.1
25.9
Total
95
65.2
48
80
6.0
36.4
c::::JGillnet, N =45
--+-Total, N = 109
50
35
45
30
40
35
25
"
30
20 ]
"C
25
~
OJ)
S
S
OJ
20
""'o
15 ~
'•"
15
10
"
1;j
-!::.-
10
5
5
0
..,.
..,., ..,.,
,
,
'"
'"
1=
'"
'" ..,.0 .... 0'"
0
'" '"
'"
'"
..,.
..,.
,
,
'"
'"
.;,
'" '"
'" 0 , '"'",
0
'"
'" '" '"
t"-
t"-
t"-
t"-
...oo,
0
oo
Total length (em)
Fig. 4.
...
'"00, '"0, .;,
'"
'"
00
'"
'" '"
..,.
-- - - -'"'"
--
....
0
0
0
,
'"0 ,
.,.,
0
0
,
,
Length distribution ofthe Greenland halibut investigatedfor fecundity.
indicate longline catches,
c:::::::J indicate giltnet catches,
indicate total length distribution of the combined fecundity sample.
N = number of individuals recorded.
7
Fecundity
Fecundity estimates ranged from ,6,800 to 70,500 eggs per female. The estimated mean,
fecundity was 28,100 eggs (std 13.7, N 95) (Tab. 2). The fecundity estimates for
Greenland halibut caught on gUlnets were slightly higher than fecundity of Greenland halibut
caught on longlines (Tab. 2).
=;
=;
The relationship between fecundity (F) and length (L) (Fig. 5) of the combined sample is:
F
=;
1.155
* 10.7 * L 4598
(r'= 0.68, p <0.005).
The fecundity is expressed as 1,000 and the length is given as total length incm.
The relationship between fecundity (F) and weight (W) (Fig. 6) of the combined sample is
given by:
F = 2.539
* 10"" *W 1,439
(r'=0. 77, p <0.005).
The fecundity is expressed as 1,000 and the total weight is in grams.
Tab. 2.
Summary table for Northeast Arctic Greenland halibut fecundity. Fecundity
expressed in ,1000 eggs.
Number registrations
Mean fecundity (1,000)
Minimum fecundity (1,000)
Maximum fecundity (1,000)
Standard deviation
Variance
Expected deviation between means
z
P(Z<~z) one-sided
Z-Critical, one-sided
P(Z<=z) two-sided
Z-Critical, two-sided
Longlines
50
22.4
6.8
67.5
12.6
146.4
0
Gillnets
45
34.5
7.8
70.5
12
144
Total
95
28.1
6.8
70.5
13.7
Output values
-4.88
5.43E-07
1.64
1.09E-06
1.96
8
P -0
,
•
'.
90
80
0
70
~
°o.
0
60
~
50
-~
""
"
"""
0
0
go
0
40
30
08 89
o o gO
o
0
o 00
20
10
8§00
o 0
00
00
0
II
0
0
§
0
0
08
0
40
45
50
55
60
70
65
75
80
85
90
Total length (em)
Fig. 5.
Fecundity (1,000) ofNortheast Arctic Greenland halibut related to total length.
F = 1.155 * 10-7 * L 4.598 (r2 = 0.68).
90
80
70
°°o. 60
50
;..,
' 6 40
""u 30
'" 20
10
0
o
~
-
o
~
o
o
o
""
o.
Fig. 6.
0
a
o.
-
0
a
0
M
a
°
°o.
'"
0
0
..;-
Total weight (g)
0
a
.ri
""
0
0
0
0
a
a
a
r--.
°°°
"".
Fecundity (1,000) ofNortheast Arctic Greenland halibut related to total weight
(g). F = 2.539 * 10-4 * W 1.439 (r2=0. 77).
Goiladosomatic index (GSI
Gonadosomatic index (GSI) is defined as the relative portion of which the ovaries constitute
of the total weight. For the combined sample, GSI was in the range 1.9-13.5%. Mean GSI was
7.5% (std = 2.2, N = 95) (Tab. 3). A weak increasing trend ofGSI related to length was
observed (Fig. 7). The GSI of Greenland halibut caught by gi1lnets was slightly higher than
the GSI for the Greenland halibut sampled from the longline catches (Tab. 3). Fecundity
9
,
-'
showed an increasing trend with increasing GSI (Fig. 8). The coefficient of correlation of the
log-log transformed data was = 0.50 (df= 94). The correlation was significant (p<0.005).
r
Tab.3.
Summary table ofgonad weight (GIfJ and gonadosomatic index (GSI) for
Greenland halibut used in the fecundity study. The results are related to fishing
gear.
Longlines
Gillnets
Total
Number registrations
50
45
95
Gonad weight, GW
Mean GW(g)
Minimum GW (g)
Maksimum GW (g)
207
36
738
286
70
640
244
36
738
Gonadosomatic index, GSI
Mean GSI (%)
Minimum GSI (%)
Maximnm ,GSI (%)
Standard deviation
7.0
1.9
13.5
2.4
8.0
4.4
12.3
1.7
7.5
1.9
13.5
2.2
• aSI long line
~
'$-
~
r Jl
c:J
16
14
12
10
8
6
4
2
0
o OSI gillnet
0..
o
0
45
50
0
,0
o.
• • ~ I~ ~1;j800~B~g
.' ~
Qoo
•
••• ••
•
•
•••
•
•
B
I..
55
60
..
I;j
0
.
0
0
0
0
••
0
~
65
70
75
80
85
90
Total length (em)
Fig. 7.
Gonadosomatic index (GSI) of Greenland halibut related to total fish length
• refers to the Greenland halibut caught by 10nglines(N = 50).
o refers to the Greenland halibut caught by gillnets (N = 45).
10
'.
80
N=95
70
0
,...., 60
0
0
0
-
q
50
~
~
.0 40
] 30
"..,
0
t.)
~
0
0
0
20
10
8
0
0
0
0
00
Q
o
0
0
0
0
0
o ~
0
O f0
0
;»tb
0
0
0
cP
0
Oo~
oO~d}r:o
o
0
0
°0 0
0
00
8
0
0
0
0
2
4
6
8
10
12
14
16
GSI (%)
Fig, 8.
Fecundity (1,000) for the combined sample of Greenland halibut related to GSI
(gonadosomatic index,%).
Hepatosomatic index (HSI)
Hepatosomatic index (HSI) describes the relative portion ofliver in each female relative to
total body weight. HSI was in the range 0.3 - 4.6% (Tab. 4). No clear trend between HSI and
total fish length was observed (Fig. 9).
Fecundity showed a weak, but increasing trend with increasing HSI (Fig. 10). Like for the
GSI-fecundity plot (Fig. 8) the scatter was wide. No significant relation between fecundity
and HSI was observed. The correlation coefficient for the log-log transformed data was
. ~=O.lO (N = 37, p>O.OS).
Summary table for liver weight and hepatosomatic index of the Greenland halibut
fecundity sample. The results are related to fishing gear.
Liver weigbt (LW)
MeanLW(g)
Minimum LW (g)
Maximum LW (g)
Hepatosomatic index, HSf
Mean HSI (%)
Number registrations
Minimum HSI (%)
Maximum HSI (%)
Standard deviation
Longlines
Gillnets
Total
104
54
218
85
2
204
88
2
218
2.7
5
2.3
32
0.3
4.6
2.4
37
0.3
4.6
1.1
1.1
1.9
3.4
0.6
11
"
6
N=37
5
,...,
'if.,
~
'"
::c:
••
4
••
.....
••
•
• • •• :
••
••
3
..
..
:
2
•
1
.-,'
...
• •
•
65
70
• •
--"
0
50
45
60
55
75
85
80
90
Total length (cm)
Fig. 9.·
Hepatosomatic index ("/0) o/Greenlarid halibut related to toialfish length.
90
80
,..., 70
0
60
°o.
50
~ 40
§
u
30
~
" 20
10
0
N=37
-
0
0
0
~
0. 0
0
0
0
0
0
0
0
0
0
..
..
00
0
o·
0
0
00
o
1
o
0
0
0
0
0
. 0
0
0
0
2
3
4
5
6
HSI(%)
Fig.JO.
Fecundity (1, 000) 0/ Northeast Arctic Greenland halibut related to HSI
(hepatosomatic index, %).
DISCUSSION
Greenland halibut included in the fecundity study were sampled in mid September 199'6; The
ovaries were mainly in maturity stage 4, which is, by defmition, eggs with a diameter 0[24mm (Nielsen & Boje 1995). Spawning had not started but was expected to occur within a
few months time. This is in accordance to egg development and results from investigations
carried out in the same area in 1996 and 1997, describing the spawning of Greenland halibut
12
"
(Albert et a/: ·1998; Stene et aL 1998), The eggs were easily classified and counted, as the
difference between GJ andG2 was obvious,
Gonadosomatic indices (GSI) ranged 2.0-135. Fedorov (1968) assumed that Greenland
halibut prior to spawning undergo an increase in gonad weight, theGSI reaching 15-18% as
spawning is likely to occur. In West Greenland waters GSI for Greenland halibut is reported
to increase from 1-3% in April-July toea. 10% in October (Jl2lrgensen & Akimoto 1990).A
study.conducted in East Greenland waters in 1997 (RI2Inneberg lit al. 1998) reported GSI in the
range 1-5%.in July.
In the Barents Sea the GSI is observed to increase from a minimum in February-April towards
spawning in November-January (Gundersen and others in prep.(a)). This verifies that the
maturity process is in progress in the period of sampling, however, not overlapping with the
time of spawning.
The fecundity of Greenland halibut showed a slightly better relationship to weight than to
length, however, both relations were significant (p<0.005). In the fecundity-Iengthrelationship the exponent b was estimated to 4.598. Bagenal (1978) stated that the exponent
may range from ea. 2.3 to 5.3, most often seen a little above 3. The exponent b is therefor in
the interval described by Bagenal (1978).
Sampling of the ovaries was random. The sampling was conducted from one longlinesetting
and one gilInet setting. The samples were taken during a multigear survey in September 1996,
and.so the sampling has been conducted over a relatively short period of time. The samples
taken from the longline catches originated from smaller females than the gillnet samples. This
reflects the actual catch performance of the gears due to selectivity, described by Nedreaas et
al. (1996). No systematic difference in the relation between fecundity and total length for fish
of the same length was observed when comparing the two gears. However, the mean
fecundity of the Greenland halibut sampled from the gillnet catches was significantly higher
than the mean fecundity of the Greenland halibut sampled from the longline catches (Tab. 2).
This is explained by the different length range of the two samples.
Prior to the study described in this paper, only a few egg counts have been conducted for
Greenland halibut in the Northeast Arctic. Millinsky (1944) estimated a fecundity of 28,000
and 33,000 for two Greenland halibut females in the Barents Sea. This is within the same
range as the results of the present study. Further analyses on the fecundity of the Greenland
halibut in the Northeast Arctic are in progress (Gundersen and others in prep. (b)).
In the Northwest Atlantic a few investigations on the fecundity of Greenland halibut have
been conducted..In the Newfoundland-Labrador area, the fecundity was in the range 15,000 to
215,000 (Lear 1970). A curved relationship based .on 45 females collected over the period
1967-1969, was established. Bowering (1980) compared the results obtained by Lear (1970)
to fecundity samples collected in the Southern LaiJrador and the South-eastern Gulf of St.
Lawrence in 1976-1978. The equation presented by Lear (1970) indicated a higher fecundity
for Greenland halibut bigger than 80cm than the equation presented by Bowering (1980). The
period of sampling for the two studies may bias the results as Lear (1970) sampled the ovaries
over the period March-October, whereas the results presented by Bowering (1980) was based
on samples collected over a shorter time period; October-November. The great time span in
13
,.
season, for the samples taken in 1967-1969, and the relatively few samples collected over
three years may give considerable variation in estimates both due to growth during the year
and annual fluctuations in fecundity.
Using the relationship betweehfecundity and.length presented in this paper a70cm female
Greenland halibut in the Barents Sea is likely to produce 35,000 eggs on average.In the
Labrador area"the fecundity~length~relationship indicated that a 70cm long female produced
.30,000 eggs on average, while a '90 cm feIIlale produced 66 000 eggs. In the Gulf of St.
Lawrence a 70cm female produced 50,000 eggs on average (Bowering 1980). This indicates a
geographic variation in fecundity. Further studies concerning this comparative aspect should
be col1ducted.
Jensen (1935) estimated the fecundity of one female (lOlcm) in West-Greenland waters to
300,000 eggs. In East Greenland waters fecundity was estimated to be in the range 32,000277,000 eggs (Renneberg et al. 1998). This is a considerably wider range offecundity than
observed for the present study.in the Barents Sea. However, the fecundity estimates presented
for East-Greenland waters (Rmmeberg et al. 1998), and Southern Labrador (Lear 1970) are
based on Greenland halibut in a wider length range, including larger fish than in the present
study. '
In Icelandic waters ovaries from 5 Greenland halibut females were analysed for fecundity in
March 1977 (Magnusson 1997).The fecundity was in the range 17,500 (66cm) to 42;200
(74cm).The largest Greenland halibut was 96cm, showing a fecundity of 37,600. The egg
diameter of the ovaries was in·the range 2-4=, which corresponds to the present study.
Fecundity for Northeast Arctic Greenland halibut showed an increasing trend with increasing
, GSI (I"' = 0.50, p<0.005). The scatter ofthefecundity-GSI plot was wide. The same was also
observed for Greenland halibut in East Greenland waters, but a correlation coefficient was not
presented (Renneberg et al. -1998). A significant relation between fecundity and HSI was not
observed. The scatter was wide, corresponding to the results from Greenland halibut in East
Greenland waters (Renneberg et al. 1998). A more comprehensive study regarding the effects
of length, weight, gonad weight, GSI, liver weight and HSI on fecundity is in progress
(Gundersen and others in prep (b)).
ACKNOWLEDGEMENT
The authors want to thank the Institute dfMaril1e Research, Bergen, Norway for finanCing the
study. The authors want to thank the staff of the vessels MIS Vonar and MIS Husby SeniOr,
the scientific staff of the Institute of Marine Research collecting thematerial and O. Espe,
M0reResearch for thorough work in the laboratory.
'
-', ,
14
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